There is a stapler including: a staple driving section in which a staple striking mechanism having a driver adapted to be driven by a motor is provided, and a cartridge loaded with a plurality of staples is attached; and a table which holds a clincher mechanism disposed so as to face staple legs that are struck from the staple driving section. In the stapler, the staple striking mechanism of the staple driving section is driven toward sheets of paper to be bound placed between the staple driving section and the table, and the staple inside the cartridge is struck toward the sheets of paper to be bound. The staple legs penetrating through the sheets of paper to be bound engage with the clincher mechanism held by the table, and are bent along a rear face of the sheets of paper to be bound, thereby carrying out a stapling.
The table holding the clincher mechanism at a front end thereof is supported at rear ends of side pieces that are integrally formed on both sides of the table in such a way as to be able to rotate with respect to a frame of the staple driving section. In a normal state, the table is rotated such that the clincher mechanism is moved away from an upper surface of the staple driving section. After the sheets of paper to be bound are placed between the clincher mechanism and the staple driving section, the table is rotated so as to hold the sheets of paper to be bound between the table and the upper surface of the staple driving section. Generally, the table needs to support the rear face of the sheets of paper to be bound with a load of about 8 to 10 kg against a binding load caused while the legs of the staple driven by the staple striking mechanism of the staple driving section penetrate through the sheets of paper to be bound and are bent along the rear face of the sheets of paper to be bound by the clincher mechanism formed at the front end of the table. Further, an operating stroke of the table varies in accordance with a thickness of the sheets of paper to be bound. For this reason, the table cannot be rotated directly by a cam, a linkage mechanism or the like. Accordingly, the table is operated with a spring force being applied to the cam or the linkage mechanism. However, a spring that can apply a large load is required in order to support the aforementioned binding load. Therefore, in order to operate the table against the large spring load, the driving mechanism itself is increased in size. As a result, downsizing of a stapler to be incorporated in a copy machine or the like is hampered.
JP-A-2001-191265 discloses a table locking device in which a table is biased by a relatively weak loading spring in a direction in which the table clamps sheets of paper to be bound with a staple driving section, a wedge member is fitted between a part of the table rotate by the spring biasing force and a frame, and the table is fixed by the wedge member in a closed position in which the table clamps the sheets of paper to be bound with the staple driving section. The table locking device includes: a table which is rotatably supported on a body case at a rear end thereof by a rotating support shaft and is biased to rotate in a closing direction by a torsion coil spring; an operating link operable to rotate the table in an opening direction and to hold the table in an open position; and a wedge operable to engage with a part of the table when the table operates in the closing direction, thereby preventing the table from rotating in the opening direction.
In the above described mechanism, during a normal state before a stapler is operated, the operating link is engaged with a rigid shaft which rotates integrally with the table, thereby holding the table in the open position. When the sheets of paper to be bound is placed on an upper surface of the staple driving section and the stapler is operated, the operating link disengages from the rigid shaft interlockingly with a staple striking mechanism which drives staples. As a result, the table is rotated in the closing direction due to the torsion coil spring, and the sheets of paper to be bound placed between the table and the staple driving section is clamped therebetween. As the table rotates in a direction in which it clamps the sheets of paper to be bound, the wedge member is slid by the spring force and engages with the rigid shaft that rotates integrally with the table. As a result, the table is prevented from rotating in the opening direction and is locked in the closed position in which the table clamps the sheets of paper to be bound.
In the table locking device of JP-A-2001-191265, rear ends of both side pieces that are integrally formed on both sides of the table are rotatably supported on the frame, and a pair of wedge members disposed adjacent to the side pieces engages with the rigid shaft that penetrates through the side pieces, whereby the table is locked in the closed position and the sheets of paper to be bound is clamped. Then, after a stapling is completed, in order to remove the bound sheets of paper from between the table and the staple driving section, it is necessary to pull out the pair of right and left wedge members from between the locked table and the frame and to rotate the table in the opening direction. At this time, since the wedge members are firmly fitted between the table and the frame, an initial load when pulling out the wedge members from between the table and the frame becomes very large. As a result, there arises a problem that a drive motor stops, or the drive motor is damaged due to a heat generated by an increase in current flowing through the drive motor.